The present invention relates to a conveyor with a frame supporting a carrier device for carrying a load. More particularly, the present invention relates to such a conveyor supported by motor-driven wheels to effect traveling movement along a predetermined track and/or the carrier device being movably supported in relation to the frame of the conveyor. Still more particularly, the present invention also relates to a plant for baling paper pulp.
It is well know in the art that driving motors for the movement of conveyors, as well as driving motors for carrier devices on the conveyor frame, can be stopped in different stop positions by the action of mechanically mounted limit positions. The limit positions communicate with contactors, for example, which activate the driving motors. When the contactors are in xe2x80x9conxe2x80x9d position the driving motors run at full speed and are stopped when the contactors, under the influence of the limit positions, are caused to assume the xe2x80x9coffxe2x80x9d position. However, movement of the conveyor and/or of the carrier device is stopped with a certain time delay, which means that precision in stopping in the path of travel of the conveyor or of the carrier device on the conveyor is generally poor. Stopping thus sometimes occurs xe2x80x9ctoo earlyxe2x80x9d in the actual movement, and sometimes xe2x80x9ctoo late.xe2x80x9d The location of the limit position in the path of travel of the conveyor and/or the limit positions of the carrier device must then be mechanically adjusted so that stopping occurs at the intended location. Adjusting the limit positions in this manner is impractical and time-consuming.
It is often desirable for the conveyor to be stopped at several points along its path of travel and/or for the carrier device to be stopped at several points in relation to the conveyor frame. It is known in the art that this can be realized by permitting the traveling movement of the conveyor, or carrier device movement, to continue for a specified time and then be stopped, which is hardly an exact method. Alternatively, several stop locations can be determined by means of limit positions arranged at these stop locations. The problems which are encountered with such an arrangement are particularly difficult in the case of the actual traveling movement of the conveyor. Limit position indicators must therefore be used to provide a number of xe2x80x9cpreparatoryxe2x80x9d limit positions before a stop position, in order to indicate that the speed must be reduced, and the driving motor must be stopped at some way considerably before the actual stop position, since the conveyor will continue its movement due to inertia. The load on the conveyor is also of significance in this regard. The conveyor must often thus be pulled to the actual stop position with the aid of hydraulic devices after the driving motor has been stopped. Another drawback is that the situation is different when the conveyor is traveling in the opposite direction. The result is that a very large number of limit positions is required. For five stop positions, for instance, thirteen limit positions are required, including preparatory limit positions.
Present technology renders it difficult to set correct stop positions for the conveyor movements since these are dependent on the performance of the driving motor, the cycle time of the control program, the friction on the rails and the total weight of the conveyor, which is also dependent on the size of the load.
Considerable precision in the movement of the conveyor is thus required for many applications, e.g. baling paper pulp. Several bales must often be placed on the carrier device one at a time. It is then of great importance that the distribution of or the spacing between the bales is always substantially the same. The bales must also be well centered on the conveyor during transfer from one conveyor to the next. The greater the precision in this respect, which is thus determined by the carrier device being stopped at the correct positions, the simpler will be subsequent handling with machines, trucks and the like.
One object of the present invention is to thus eliminate the above-discussed drawbacks in known conveyors.
In accordance with the present invention, this and other objects have now been realized by the invention of a conveyor system comprising a conveyor including carrier means for carrying a predetermined load, a frame for the carrier means, a track, wheel members supporting the frame for movement along the track from a predetermined reference position, and sensor means for detecting a position of the conveyor along the track with respect to the predetermined reference position without direct contact therewith, the sensor means delivering a train of pulses corresponding to a predetermined distance of movement of the conveyor along the track, whereby the position of the conveyor along the track can be determined. In a preferred embodiment, the conveyor system includes a driving motor for moving the conveyor along the track, and the sensor means are positioned to detect the rotation of the wheel members along the track or the rotation of the driving motor.
In accordance with one embodiment of the conveyor system of the present invention, the conveyor system includes a plurality of detection points disposed along the track for detection by the sensor means. Preferably, the plurality of detection points comprise a plurality of openings evenly spaced along the track.
In accordance with another embodiment of the conveyor system of the present invention, the conveyor system includes speed control means for controlling the speed of movement of the conveyor along the track based upon the train of pulses determined by the sensor means.
In accordance with another embodiment of the conveyor system of the present invention, the carrier means comprises a chain conveyor.
In accordance with another embodiment of the conveyor system of the present invention, the driving motor comprises a reversible driving motor, whereby the direction of movement of the conveyor along the track can be reversed.
In accordance with another embodiment of the conveyor system of the present invention, the sensor means comprises conductive pulse transducer means for detecting conductive changes and determining the corresponding train of pulses based thereon.
In accordance with another embodiment of the conveyor system of the present invention, the conveyor system is used in the baling of paper pulp.
In accordance with the present invention, a conveyor system has been discovered which comprises a conveyor including carrier means for carrying a predetermined load, a frame for the carrier means, the carrier means being movably supported on the frame for movement from a predetermined reference position, and sensor means for detecting the position of the conveyor means with respect to the predetermined reference position without direct contact therewith, the sensor means delivering a train of pulses corresponding to a predetermined distance of movement of the carrier means with respect to the frame, whereby the position of the carrier means can be determined. In a preferred embodiment, the conveyor system includes a plurality of motor driven gear wheels for movably supporting the carrier means with respect to the frame. Preferably, the conveyor system includes a driving motor for driving the motor driven gear wheels, and the sensor means are positioned to detect the rotation of the motor driven gear wheels or the rotation of the motor.
In accordance with one embodiment of the conveyor system of the present invention, the conveyor system includes a plurality of detection points disposed along the carrier means for detection by the sensor means. Preferably, the plurality of detection points comprises a plurality of openings evenly spaced along the carrier means.
In accordance with another embodiment of the conveyor system of the present invention, the conveyor system includes speed control means for controlling the speed of movement of the carrier means along the frame based upon the train of pulses determined by the sensor means.
In accordance with another embodiment of the conveyor system of the present invention, the driving motor comprises a reversible driving motor whereby the direction of movement of the carrier means with respect to the frame can be reversed.
In accordance with another embodiment of the conveyor system of the present invention, the conveyor system includes a plurality of end position indicators for stopping movement of the carrier means along the frame at predetermined end positions.
In accordance with another embodiment of the conveyor system of the present invention, the sensor means comprise inductive pulse transducer means for detecting inductive changes and determining the corresponding train of pulses based thereon.
In accordance with another embodiment of the conveyor system of the present invention, the conveyor system is used in the baling of paper pulp.
In accordance with the conveyor system of the present invention, traveling movement is determined from a zero or reference position and sensors are arranged for contactless detection of the position of the conveyor on the track by counting pulses, one pulse corresponding to a certain distance. The direction of movement of the driving motor is also known.
In accordance with a preferred embodiment of the present invention, the position of the conveyor can be detected by measuring the rotation of the driving motor or the wheels. The position can also be measured with the aid of points along the track of the conveyor, in the form of openings spaced evenly along a strip, which the sensor thus detects. Alternatively, the strip may be provided with light and dark lines or bands which are detected one after another by a sensor on the conveyor or carrier device in order to sense movement in this manner. The above-mentioned technology, with fixed points, lines or the like along the path of movement provides a reliable way of determining the position of the conveyor since the actual position is detected, as opposed to the case where the position is determined from the rotation of the driving motor or wheels. If the wheels were to slip in the latter case, for instance, determination of the position would be incorrect.
In accordance with the present invention, the position of the carrier device can be detected by measuring the rotation of the driving motor or of the gear wheels. Only one limit position is thus required at each end of the carrier device in order to obtain starting points to determine the relative position of the carrier device after the load has influenced the limit position.
The conveyor system in accordance with the present invention offers not only functional improvements but also advantages from the points of view of both manufacturing and installation. With the conveyor system in accordance with the present invention the stop positions are thus determined by means of software instead of physically, as with previously known technology. This means that all conveyors can be made the same, thereby facilitating standardization, thus improving manufacture. Installation and start-up of the conveyor movements can now be performed more quickly, since no physical stop positions need be moved and adjusted, and the load on the conveyor carrier device can be taken into consideration when controlling the movements of the conveyor.
The pulse transducer technology in accordance with the present invention is also well suited for use in connection with so-called frequency operation of the driving motors. During such frequency operation the speed of the driving motor is controlled by means of pulses which have varying on and off times. The motor speed can thus be optionally controlled from standstill up to full speed, and smooth starting and stopping movements can be achieved so the load is not displaced. Higher speeds can be used for movements of the conveyor, and the speed can be gradually reduced so that the desired stop position is reached exactly. The capacity of the plant is also increased in relation to known technology if conveyors comprising pulse transducer technology are used in a baling line, for instance.
According to an advantageous embodiment of the conveyor system in accordance with the present invention, the sensors comprise inductive pulse transducers which are arranged to detect inductive changes when the wheels or driving motors are rotating. These pulse transducers are extremely reliable and are particularly well suited for industrial applications, and since detection occurs contactless, there is no wear or abrasion. The pulse transducers are accurate and are protected from vibrations, dampness and dirt, and can therefore be advantageously used in difficult environments.
The invention present also relates to a plant for baling paper pulp.